System and Methods for Assessing Whole-Building Thermal Performance

ABSTRACT

An assessment system and method are described that capture indoor temperature measurements and corresponding outdoor temperature measurements in order to determine a thermal efficiency of a structure. The assessment system identifies quiescent periods and trims these periods to eliminate undesirable influences such as auxiliary heating or solar gain. The quiescent periods are then compared to outdoor temperature differences to determine the thermal efficiency of the structure. The system can model the structure&#39;s performance metrics, through inferred qualitative and quantitative characterizations including, but not limited to, the building&#39;s rate of temperature change as a function of internal and external temperatures, the building&#39;s heating, cooling, and other energy needs as they relate to the building envelope, appliances, and other products used at the site and occupant behavior.

RELATED APPLICATION DATA

This application is a continuation of U.S. application Ser. No.14/213,105 filed Mar. 14, 2014 and titled “System and Methods forAssessing Whole-Building Performance” and claims the benefit of priorityof U.S. Provisional Patent Application No. 61/792,843 filed Mar. 15,2013, and titled “System and Method for Assessing Whole-Building ThermalPerformance”, both of which are incorporated by reference.

FIELD OF THE INVENTION

The present invention generally relates to systems and methods forevaluating the energy efficiency and/or thermal characteristics ofstructures. In particular, the present invention is directed to Systemsand Methods for Assessing Whole Building Thermal Performance.

BACKGROUND

Methods for evaluation of the energy performance of structures, e.g.,office buildings, homes, apartments, etc., are of significant importancebecause, without an understanding of a structure's performance, it ischallenging to determine whether improvements will lead to significantbenefits to the structure's owner or occupants.

Understanding a structure's thermal efficiency well after commissioningand in older structures is also challenging because the buildingmaterials deteriorate over time. For example, insulation and sealsaround windows of a building may deteriorate over time due to exposureto harsh conditions such as ultraviolet rays from the sun and otherharsh weather conditions like rain, wind, snow, and ice. Aging and theaforementioned conditions cause the building materials to lose theireffectiveness as insulators and barriers against moisture and air andthereby contribute to decreased energy efficiency of a building.However, determining how these factors affect the structure's thermalefficiency, in a cost-effective has proved elusive.

Methods and systems have been developed to evaluate the energyperformance or thermal efficiency of structures, but these methods andsystems require complicated, high technology systems; intense dataintake and controls; and/or particular conditions in order to obtainadequate measurements. Because of these aforementioned characteristics,these systems are practically useless for existing structure owners andthe contractors they may hire to understand/improve their structure'sefficiency. Accordingly, there is a need in the art for a system andmethod which can provide useful baseline energy metrics from which abuilding occupant can compare their building against without the needfor specialized equipment, extensive data collection, and/ornon-standard conditions to conduct the data acquisition.

SUMMARY OF THE DISCLOSURE

In a first exemplary aspect a system for characterizing a thermalefficiency of a structure comprises: a measurement device for recordingan inside temperature of the structure; a first database includingperiodic outside temperature measurements proximate the structure; asecond database in communication with the measurement device and thefirst database, the second database configured to receive, as inputs,the inside temperature and the outside temperature and to correlate theinside temperature and the outside temperature; and a processor incommunication with the second database and capable of executing a set ofinstructions, the set of instructions including: determining adifference between the inside temperature and the outside temperature;determining a plurality of quiescent periods from the insidetemperature; determining a rate of change during each of the pluralityof quiescent periods; comparing the rate of change with the difference;and determining a thermal efficiency of the structure from thecomparing.

In another exemplary aspect, a context-based thermal efficiencydetermination system for a structure comprises: a data acquisitiondevice capable of recording or receiving a raw data set including aninside temperature, a set-point, a heating data, an outside temperature,a weather metric, and an occupancy metric; and an analysis moduledetermining, based upon the raw data set, a plurality of quiescentperiods, wherein the plurality of quiescent periods includes a pluralityof divergent quiescent periods and a plurality of non-divergentquiescent periods; a thermal efficiency module determining a thermalefficiency of the structure based upon the plurality of non-divergentquiescent periods.

A method of characterizing a thermal efficiency of a structurecomprising: collecting temperature data from inside the structure andoutside the structure; determining a difference between the temperatureinside the structure and outside the structure; determining, from theinside temperature data, a plurality of quiescent periods; determining arate of change during each of the plurality of quiescent periods;relating the rate of change to the corresponding differences intemperature inside the structure and outside the structure; anddetermining, from the relating, a thermal efficiency of the structure.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating the invention, the drawings show aspectsof one or more embodiments of the invention. However, it should beunderstood that the present invention is not limited to the precisearrangements and instrumentalities shown in the drawings, wherein:

FIG. 1 is a graph of indoor temperature versus time;

FIG. 2 is another graph of indoor temperature versus time;

FIG. 3 is a graph of indoor temperature and a corresponding outdoortemperature versus time;

FIG. 4 is a graph of the rate of temperature change versus thedifference between the indoor temperature and outdoor temperatureaccording to an embodiment of the present invention;

FIG. 5 is a block diagram of an assessment system according to anembodiment of the present invention;

FIG. 6 is a block diagram of an exemplary method of determine thethermal efficiency of a structure according to an embodiment of thepresent invention; and

FIG. 7 is a block diagram of a computing environment that may be used toimplement an assessment system according to an embodiment of the presentinvention.

DESCRIPTION OF THE DISCLOSURE

A system and method of assessing whole-building thermal performance ofthe present disclosure collects indoor temperature measurements and thetime associated with those measurements and isolates quiescent period(s)for analysis of rate of change in temperature inside the structure(i.e., heating or cooling) in conjunction with the difference betweenthe indoor and external temperatures and provides a measurement ofbuilding efficiency. The system can model the building's performancemetric(s), through inferred qualitative and quantitativecharacterizations including, but not limited to, the building's rate oftemperature change as a function of internal and external temperatures,the building's heating, cooling, and other energy needs as they relateto the building envelope, appliances, and other products used at thesite and occupant behavior. The system can also adjust the performancemetric(s) using time-stamped hourly or sub-hourly interval electricconsumption measurements such as could be obtained by electric utility“smart meters” or a comparable device as an indication of internalthermal gains in the building. The system can also correlate theperformance metrics with, for example, the thermal characteristics ofthe building shell, so as to estimate heat losses through comparison andanalysis to energy performance data, calibrate for useful energyconsumption, identify building shell savings opportunities, identifyusage behavior savings, identify equipment performance upgradeopportunities, and verify savings from energy efficiency improvements.

Turning now to the figures, FIG. 1 shows a graph 100 that plots theinside temperature measurements 104 of a structure over several days.The inside temperature changes occurring within a structure are causedby a number of factors, including, but not limited to, heating orcooling units, occupancy, heat emitting devices (e.g., lights,electronics, ovens, etc.), solar heating, weather events, etc. As shownin FIG. 1, the structure experiences low temperature readings of about58° F. and 54° F. degrees during the period of measurement and hightemperature measurements of about 68° F. degrees. The structure alsoexperiences a number of relatively rapid alternating changes intemperature, designated as regions 108A and 108B, as well as periods ofrelatively constant decline, e.g., quiescent periods 112A-C. Quiescentperiods 112A-C represent periods of relative inactivity within thestructure and are indicative of the thermal efficiency of the structurewhen evaluated with additional information as discussed in more detailbelow.

FIG. 2 is a graph 200 of temperature over time, with the temperaturemeasurements being taken at 5 minute intervals (represented by a coolingline 204) during a gradual cooling period, such as, for example,quiescent region 112A. As shown, cooling line 204 gradually decreasesfrom about 67° F. to about 63° F. over a span of about 3 hours. Coolingline 204, although not decreasing at a constant rate, cooling line 204is representative of the heat losses in the structure over this timeframe.

The rate of decrease of cooling line 204 is influenced by severalfactors, but primarily the temperature outside the structure. FIG. 3 isa graph 300 showing temperature measurements inside the structure,represented by inside temperature line 304, the temperature measurementsoutside the structure, represented by outside temperature line 308, overtime. Inside temperature line 304 has some similarities to that ofinside temperature measurements 104 (FIG. 1) in that it includes regionsof relatively rapid alternating changes in temperature, regions 312A-D,and quiescent periods 316A-E. Regions 312A-D can represent periods whereheating/cooling systems are attempting to maintain a constanttemperature within the structure in response to requests by occupants ofthe structure. Thus, the heating/cooling system cycles on and off toprovide, in this example, heat to the inside of the structure inresponse to heat losses by the structure. When the occupants of thestructure are away or chose to have lower inside temperatures, thestructure's heating/cooling system does not turn on for extended periodsand during these periods there can be relatively constant heat losses(or gains depending on the external temperatures), i.e., quiescentperiods 316A-E. Quiescent periods 316, when correlated with other data,can provide a performance metric related to the structure's thermalefficiency. However, and as explained in more detail below, not allquiescent periods 316 should be used to evaluate the thermal efficiencyof a structure. Certain quiescent periods 316, referred to herein asdivergent quiescent periods, should be excluded due to influences thatimpact that rate of temperature change, e.g., weather events, poor dataavailability, occupancy changes, etc. As shown in FIG. 3, non-divergentquiescent periods 320A-D (corresponding to quiescent periods 316A-D) arequiescent periods without significant thermal influences, whereas anidentified divergent quiescent period 324 (corresponding to quiescentperiod 316E) has such influences (note the shallower slope of quiescentperiod 316E when compared to 316E despite continuous decreasing outsidetemperatures, which may be indicative of, for example, solar heat gain).

As evident from graph 300, the temperature outside the structureinfluences the temperature inside the structure. Thus, as the outsidetemperature drops, the rate of decrease of quiescent regions 316increases. For example, it is apparent that quiescent region 316Aoccurring at an outside temperature of about 40° F. decreases at aslower rate (shallower slope) than quiescent region 316D occurring at anoutside temperature of between 10° F. and 0° F.

FIG. 4 is a graph 400 of the rate of change of the temperature (° F./hr)versus the difference between the inside temperature of the structureand the outside temperature of the structure (ΔT). The relationshipbetween the rate of change of each quiescent region 316 and thedifferences between the inside and outside temperature provides insightinto the thermal efficiency of structure and is discussed in more detailbelow. As shown in FIG. 4, trend line 404 indicates the aforementionedrelationship that forms a part of the system and method of the presentdisclosure.

Turning now to a discussion of the components of a system for assessingstructure thermal performance (hereinafter, “assessment system”)according to the present disclosure and with reference to FIG. 5, thereis shown an exemplary assessment system 500. Assessment system 500includes, at a high level a measurement device 504, a first database508, a database 512, and a processor 516.

At a high level, measurement device 504 monitors and reports the insidetemperature of the structure and also provides a time-stamp associatedwith the measurement. In an exemplary embodiment, measurement device 504is a “smart” thermostat, capable of sending collected data related tothe temperature of the structure as well as any defined temperatureset-points, and receiving data inputs, although no special conditions(e.g., controls, steady-state conditions, etc.) are required in order toreceive data of sufficient quality for inclusion in assessment system500. Also, although the system can accommodate rapid/continuousmonitoring by measurement device 504, there is not a need for intensivemonitoring of temperature inside the structure. For example, in anexemplary embodiment, measurement device 504 records a temperaturemeasurement in about 5 minute intervals. In another exemplaryembodiment, measurement device 504 records temperature measurement atvariable lengths intervals. In this embodiment, the variable lengthintervals can range from 4 to 60 minutes in length.

In an alternative embodiment, measurement device 504 is a temperaturesensor such as, but not limited to, a thermocouple, a thermistor, aresistance thermometer and a silicon band gap temperature sensor, thattransmits a signal representative of the temperature of the inside ofthe structure to, for example, first database 508, which applies thetime-stamp when the signal is received. Measurement device 504 can be awired or wireless device and can be configured to monitor, record,store, or transmit data, including, but not limited to, temperaturedata, humidity, HVAC system status, and occupancy. In another exemplaryembodiment, more than one measurement device 504 is employed withinassessment system 504. In other exemplary embodiments, measurementdevice 504 can collect additional inputs, such as, but not limited to, atemperature set-point, a building characteristic such as heating systeminformation, an electrical information, and a demographic informationassociated with the building. Assessment system 500 can include aplurality of measurement devices 504 (not shown), or a singlemeasurement device capable of sensing multiple types of data.

First database 508 receives and stores data received from measurementdevice 504. As discussed above, in certain embodiments, first database508 may include additional information upon receipt of data frommeasurement device 504. For example, first database 508 may apply atime-stamp indicating the time of receipt of the data from measurementdevice 504. As another example, first database may include informationsuch as, which measurement device 504 (in the case that multiple devicesare employed with assessment system 500) provided the data. Firstdatabase 508 stores the data in a format and organization compatiblewith future uses of the data contained therein.

Second database 512 is configured to receives and stores data fromthird-parties, such as, but not limited to, weather station data (e.g.,wind, temperature, sun movements, etc.) 516, utility data 520, andstructure information 524, or other measurement devices external to thestructure. As with first database 508, second database 512 may includeadditional information upon receipt of data from the third-parties. Forexample, second database 512 may apply a time-stamp indicating the timeof receipt of the data from third-parties. While first database 508 andsecond database 512 are described separately, the two databases could becombined into a single database or be a part of a data acquisitiondevice configured to perform the functions of the databases as describedherein.

Data stored in first database 508 and second database 512 is evaluatedusing instructions included within processor 516. The instructionsincluded within processor 516 perform analyses on the data received fromfirst database 508 and second database 512 in order to generate athermal efficiency value for the structure. In an exemplary embodiment,processor 516 determines the differences between the inside temperaturemeasurements and the outside temperature measurements of the structure.In this embodiment, the inside temperature measurements are recorded bymeasurement device 504, as discussed above, and the outside temperaturemeasurements are provided by a third-party source, such as weatherstation 516. The difference between the two measurements are time-based,with the understanding that the time of collection of the insidetemperature may deviate from the time of collection by the third-partyand the deviation being reconciled by processor 516 using methodsdescribed herein.

Processor 516 also determines the quiescent periods, such as quiescentperiods 316A-E, that occurred within the structure from the insidetemperature measurements. Generally, quiescent periods are those periodsin which the inside temperature shows a relatively constant decrease (orincrease depending on the temperature outside the structure) over aperiod of time. In an exemplary embodiment, the period of timesufficient for determining a quiescent periods is about 4 hours, butcould be as short as about 2 hours. After identifying one or morequiescent periods, processor 516 determines the rate of change duringeach of the quiescent periods identified and then compares the rate ofchange with the difference in temperature between the inside and outsideof the structure during the time-period of the rate of change. From thiscomparison, a thermal efficiency of the structure is deduced bygenerating a linear regression of the quiescent periods with the averageindoor-outdoor temperature difference being used as predictor of theheat loss rate of the structure (as shown in FIG. 4). The slope of thelinear regression is a measure of the thermal efficiency of thestructure, i.e., a more thermally efficient structure will have ashallower slope than a less thermally efficient structure, assumingsimilar surface area-to-volume ratios of the structure.

Processor 516 may also be capable of identifying and filtering outauxiliary heating and other events, by recognizing the occurrence ofsuch events occurring with the structure. For example, if during aquiescent period, the inside temperature of the structure rises or fallsoutside of the thermostatic set-point dead-band, this can be used as anindicator of space heating or cooling provided by secondary (ornon-thermostat controlled) sources like a wood stove or a room airconditioner. These quiescent periods can then be removed from theanalysis to provide a more accurate assessment of building thermalefficiency. Similarly, processor 516 can filter out events such as solargains, window and door heat losses, fans, occupant activities, andthermal mass effects using similar methods as described just above. Forexample, heating or cooling is often represented in the data by smooth,continuous curves and thermal mass effects are discernible when theslope of the temperature change during the quiescent period deviatesfrom an established normal rate. As another example, information insecond database 512, such as utility data, can be used to filter outparticular quiescent periods that show internal thermal gains due toelectric energy use or other measureable factors.

Assessment system 500 is also adaptable to multi-zonedwellings/structures. For example, by using data, such as, but notlimited to, square footage, occupancy, and other information asindicated above, unified building performance metrics can be obtained.In one embodiment, the collected data is weighted, integrated, andcombined with trend data from each zone of the multi-zone structure toproduce one or more performance metrics.

Alterative embodiments of system 500 can provide the ability to:

-   -   1. Recognize and characterize variances in site metrics to serve        as indicators of changed energy usage, and/or efficiency at the        site.    -   2. Allow for Customer engagement through display (on device,        mobile app, website, e-mail, or direct mail) of site-specific        insights derived through the above and the following:        -   a. QA/QC (also Evaluation, Measurement and Verification) of            thermal efficiency-related work and changes (contractor or            DIY).        -   b. Homeowner usage behavior assessment to support energy            savings estimates and guarantees, calibration of energy            consumption estimates and benchmarking.        -   c. Duty-cycle of steady state heating (system sizing, short            cycling losses, over-sizing, underperformance, and other            faults and inadequacies in heating systems).        -   d. Estimating energy impacts (potential or actual) of            controls, behavioral, and system changes.        -   e. Estimating improvement in building envelope performance            in completed weatherization projects.

Turning now to an exemplary method 600 of determining the thermalefficiency of a structure, with reference to FIGS. 1-5 and with furtherreference to FIG. 6, at step 604 a set of data points representative ofa temperature inside the structure is collected. In an exemplaryembodiment the data points include a timestamp indicative of the timethe temperature was taken.

At step 608, outdoor temperature data is collected, the outdoortemperature data being data that is at least proximate the structure,e.g., similar area, town, zipcode. In an exemplary embodiment, outdoortemperature data is collected from a nearby National Weather Service(NWS) station, preferably in classes I, II, or III.

At step 612, the outdoor temperature measured closest to the same timeas the indoor measurement is determined. In an exemplary embodiment, alinear interpolation of the outdoor temperature data is performed inorder to ascertain the outdoor temperature at the same time as theindoor temperature measurement time. In another embodiment, thetemporally closest outdoor temperature value to that of the indoortemperature measurement time is determined.

At step 616, the mean rate of indoor temperature change (i.e., the speedof heat loss or gain) between consecutive indoor temperaturemeasurements is determined. In an exemplary embodiment, the mean rate isdetermined by creating a model of the mean rate of the indoortemperature change as a linear interpolation, i.e., as a series of linesbetween consecutive points. The average of the slopes of the series oflines is the mean rate.

At step 620, quiescent periods are identified. In an exemplaryembodiment, quiescent periods are identified as those periods ofcontinuous heat loss (or gain), e.g., consecutive sequences of negative(or positive) slopes determined in step 616.

At step 624, the mean outdoor temperature during the same period as thequiescent period determined in 620 used in step 616 is determined. In anexemplary embodiment, the mean outside temperature during each segmentis the average of the outdoor temperature measurements associated withthe start and end of the segments identified in step 616.

At step 628 certain segments (determined in step 616) of the quiescentperiods are trimmed or filtered out. Exemplary trimming can include:assuming that segments which occur between dawn and dusk are biased bysolar gain and therefore their slopes are unreliable estimators of thethermal envelope; discarding segments in the first hour of any quiescentperiod as these often contain anomalous behavior, possibly due toresidual and transient behaviors of the ambient air in response to thechange in operating conditions; and/or discarding the final segment ofeach quiescent period as these segments often contain the time at whichthe heating (or cooling) system reactivates and begins to warm (cool)the air, and so even if on average negative (positive) -sloped, thatslope may be rendered smaller in magnitude the expected because ofheating (cooling) by the heating (cooling) system. In an exemplaryembodiment, any quiescent periods having two or fewer segments areremoved, then with each quiescent period that survives, the first hourof the quiescent period and last segment of every quiescent period istrimmed off the quiescent period.

At step 632 the differences between the indoor and outdoor temperaturesduring each quiescent periods (at the quiescent period midpoint) isdetermined.

At step 636 a thermal efficiency of the structure is determined bygenerating a linear regression of the quiescent periods with the meandifferences between indoor and outdoor temperature (as determined atstep 628) being used as predictor of the heat loss rate of thestructure. The slope of the linear regression is a measure of thethermal efficiency of the structure, i.e., a more thermally efficientstructure will have a shallower slope than a less thermally efficientstructure, assuming similar surface area-to-volume ratios of thestructure. Notably, the y-intercept of the regression (the outdoortemperature at which heat loss rate is 0) represents the balancetemperature. A lower balance temperature indicates a structure whicheither is better-performing or has more internal heating.

FIG. 7 shows a diagrammatic representation of one implementation of amachine/computing device 700 that can be used to implement a set ofinstructions to perform any one or more of the aspects and/ormethodologies of the present disclosure. Device 700 includes a processor705 and a memory 710 that communicate with each other, and with othercomponents, such as measurement device 504, via a bus 715. Bus 715 mayinclude any of several types of communication structures including, butnot limited to, a memory bus, a memory controller, a peripheral bus, alocal bus, and any combinations thereof, using any of a variety ofarchitectures.

Memory 710 may include various components (e.g., machine-readable media)including, but not limited to, a random access memory component (e.g, astatic RAM “SRAM”, a dynamic RAM “DRAM”, etc.), a read-only component,and any combinations thereof. In one example, a basic input/outputsystem 720 (BIOS), including basic routines that help to transferinformation between elements within device 700, such as during start-up,may be stored in memory 710. Memory 710 may also include (e.g., storedon one or more machine-readable media) instructions (e.g., software) 725embodying any one or more of the aspects and/or methodologies of thepresent disclosure, such as the instructions carried out by processor516 described above. In another example, memory 710 may further includeany number of program modules including, but not limited to, anoperating system, one or more application programs, other programmodules, program data, and any combinations thereof.

Device 700 may also include a storage device 730. Examples of a storagedevice (e.g., storage device 730) include, but are not limited to, ahard disk drive for reading from and/or writing to a hard disk, amagnetic disk drive for reading from and/or writing to a removablemagnetic disk, an optical disk drive for reading from and/or writing toan optical media (e.g., a CD, a DVD, etc.), a solid-state memory device,and any combinations thereof. Storage device 730 may be connected to bus715 by an appropriate interface (not shown). Example interfaces include,but are not limited to, SCSI, advanced technology attachment (ATA),serial ATA, universal serial bus (USB), IEEE 7395 (FIREWIRE), and anycombinations thereof. In one example, storage device 730 may beremovably interfaced with device 700 (e.g., via an external portconnector (not shown)). Particularly, storage device 730 and anassociated non-transitory machine-readable medium 735 may providenonvolatile and/or volatile storage of machine-readable instructions,data structures, program modules, and/or other data for device 700. Inone example, instructions 725 may reside, completely or partially,within non-transitory machine-readable medium 735. In another example,instructions 725 may reside, completely or partially, within processor705.

Device 700 may also include a connection to one or more systems ormodules included with assessment system 500. Any system or device may beinterfaced to bus 715 via any of a variety of interfaces (not shown)including, but not limited to, a serial interface, a parallel interface,a game port, a USB interface, a FIREWIRE interface, a direct connectionto bus 715, and any combinations thereof. Alternatively, in one example,a user of device 700 may enter commands and/or other information intodevice 700 via an input device (not shown). Examples of an input deviceinclude, but are not limited to, an alpha-numeric input device (e.g., akeyboard), a pointing device, a joystick, a gamepad, an audio inputdevice (e.g., a microphone, a voice response system, etc.), a cursorcontrol device (e.g., a mouse), a touchpad, an optical scanner, a videocapture device (e.g., a still camera, a video camera), a touchscreen,and any combinations thereof.

A user may also input commands and/or other information to device 700via storage device 730 (e.g., a removable disk drive, a flash drive,etc.) and/or a network interface device 745. A network interface device,such as network interface device 745, may be utilized for connectingdevice 700 to one or more of a variety of networks, such as network 750,and one or more remote devices 755 connected thereto. Examples of anetwork interface device include, but are not limited to, a networkinterface card, a modem, and any combination thereof. Examples of anetwork include, but are not limited to, a wide area network (e.g., theInternet, an enterprise network), a local area network (e.g., a networkassociated with an office, a building, a campus, or other relativelysmall geographic space), a telephone network, a direct connectionbetween two computing devices, and any combinations thereof. A network,such as network 750, may employ a wired and/or a wireless mode ofcommunication. In general, any network topology may be used. Information(e.g., data, instructions 725, etc.) may be communicated to and/or fromdevice 700 via network interface device 755.

Device 700 may further include a video display adapter 760 forcommunicating a displayable image to a display device 765. Examples of adisplay device 765 include, but are not limited to, a liquid crystaldisplay (LCD), a cathode ray tube (CRT), a plasma display, and anycombinations thereof.

In addition to display device 765, device 700 may include a connectionto one or more other peripheral output devices including, but notlimited to, an audio speaker, a printer, and any combinations thereof.Peripheral output devices may be connected to bus 715 via a peripheralinterface 770. Examples of a peripheral interface include, but are notlimited to, a serial port, a USB connection, a FIREWIRE connection, aparallel connection, a wireless connection, and any combinationsthereof.

A digitizer (not shown) and an accompanying pen/stylus, if needed, maybe included in order to digitally capture freehand input. A pendigitizer may be separately configured or coextensive with a displayarea of display device 765. Accordingly, a digitizer may be integratedwith display device 765, or may exist as a separate device overlaying orotherwise appended to display device 765.

Exemplary embodiments have been disclosed above and illustrated in theaccompanying drawings. It will be understood by those skilled in the artthat various changes, omissions, and additions may be made to that whichis specifically disclosed herein without departing from the spirit andscope of the present invention.

What is claimed is:
 1. A system for characterizing a thermal efficiency of a structure based upon the inside temperature of the structure and periodic outside temperature measurements proximate the structure, the system comprising: a database configured to receive, as inputs, the inside temperature and the periodic outside temperature measurements and to correlate the inside temperature and the periodic outside temperature measurements; and a processor in communication with the database and capable of executing a set of instructions, the set of instructions including: determining a difference between the inside temperature and the outside temperature; determining a plurality of quiescent periods from the inside temperature; determining a rate of change during each of the plurality of quiescent periods; comparing the rate of change with the difference; and determining a thermal efficiency of the structure from the comparing.
 2. A system according to claim 1, wherein the periodic outside temperature measurements are weather data from a third-party source.
 3. A system according to claim 1, further including a sensor proximate the structure, the sensor configured to transmit a signal representative of a temperature external to the structure, and wherein the periodic outside temperature measurements are received from the sensor.
 4. A system according to claim 1, wherein the processor includes a filtering module and certain ones of the plurality of quiescent periods are eliminated using the filtering module.
 5. A system according to claim 4, wherein the processor determines a typical quiescent period for a given difference and the filtering module correlates the difference with the given difference so as to eliminate certain ones of the plurality of quiescent periods that deviate from the typical quiescent period at the given difference.
 6. A system according to claim 4, wherein the filtering module identifies heating or cooling cycles and eliminates certain ones of the plurality of quiescent periods including the heating or cooling cycles.
 7. A system according to claim 4, wherein the filtering module identifies auxiliary heating occurring within the structure and eliminates certain ones of the plurality of quiescent periods including the heating or cooling cycles.
 8. A system according to claim 1, further including a measurement device and wherein the measurement device records the inside temperature at predefined time periods, and wherein the predefined time periods are greater than about 5 minutes.
 9. A system according to claim 1, further including a measurement device and wherein the measurement device records the inside temperature at variable time periods and wherein the variable time periods are greater than about 4 minutes. 